Tag Archives: Kepler-64

A Thousand Planets

Depending on where you get your information from and how much weight you lend it, we have reached a thousand known planets.

Some of the semi-official sites like exoplanet.eu and more official sites like NASA’s Exoplanet Archive show less than this number. In the case of the latter because it appears they only accept planets that have made it past peer review, which is a reasonable, if not high, standard. In the case of exoplanet.eu, while it has been a valuable asset since 1995, it has missed a few planets here and there as time has gone on (especially during a recent overhaul of the site). There’s a number of other anomalies there, but it’s a site run by a guy in his spare time so there’s a limit to how much you can expect of it. That being said, it’s still a very valuable resource.

There exists a fairly small group of people, myself shamelessly included, who keep tabs on extrasolar planet news and developments nearly religiously. The count varies from person to person, but I am not alone in asserting that there are now 1,000 known planets. By my count, we’ve passed that a couple months ago, but I’ve decided to give it more time to help cover some margin for error in the planet count.

Where does this margin of error arise? There’s a number of planets whose disposition is not very clear. They have been proposed and later disputed, but not fully disproven. There are planets that are unconfirmed, but confident enough that they can be talked about as real planets. And lastly there are Kepler candidates that have been determined to be planets, but in some cases have not even been included in a preprint on arXiv yet. As such, it is not possible for me or anyone to point to a specific planet and say “this is the thousandth known planet.”

In the big picture, humanity’s first thousand planets is only the top layer of H2O molecules of the iceburg of the planet population in the Galaxy. It is severely plagued by biases in favour of short-period and/or high-mass planets due to the nature of our detection methods and completeness of our detection surveys. We have found many hot Jupiters, but we know full well that this is a minority (less than 1% of stars have a hot Jupiter). It’s clear that small planets are more prevalent, it’s just a matter of detecting them.

Recently, it was announced that the nearby M dwarf GJ 667C hosts three super-Earths in its habitable zone. Taken together with the two habitable planet candidates at Kepler-64 and single habitable planet candidates in other systems, we have about a dozen targets for a search for life. Some of these planets are better candidates than others, and I won’t encourage any undue optimism by refraining from being outright by saying that some of them appear pretty unlikely candidates – a few of them look like we’re scraping the bottom of the barrel in desperate hope (I’m looking at you, HD 40307 g, GJ 163 c, Kepler-22 b, GJ 581 d).

Still, the fact that our first thousand planets contains at least a few planets where it’s not impossible for life to exist there is encouraging, especially when considering how biased our detection methods are against them. Combined with Kepler data that tells us that habitable planets are ubiquitous in the Galaxy, I am actually quite optimistic about the odds for there being a second biosphere in the solar neighbourhood.

We have learned so much in the first thousand planets, detected at a slow rate at first, but growing to over a hundred per year. It has taken us 20 years to detect the first thousand exoplanets. I would not be surprised if the next thousand come in only five years and feature many more habitable planet candidates.

Lastly, I have been dealing with some events in my “personal life” that have kept me busy, and so I have had less time to focous on extrasolar planet science and writing about it here. This is partly why this post doesn’t have a lot of meat to it. I look forward to writing more enlightening posts in the near future.

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2012 Review

An Earth-mass planet orbiting Alpha Centauri B. Credit:ESO

2012 brought us yet another remarkable year of extrasolar planet science. While the planet catch for 2012 was a little less than last year’s, the quality and importance of planets revealed this year was amazing. By far the most major results have been the discovery of an ~Earth-mass planetary companion orbiting the secondary component of the nearest star system to our own, Alpha Centauri (see here), and evidence for a system of planets around the nearby star Tau Ceti (see here). I hesitate to draw conclusions from a small amount of data, but the discovery of a terrestrial planet at none other than our nearest neighbour seems to really emphasize the point that terrestrial planets are likely as common as dirt.

A nice system of planets was reported at Gliese 676A consisting of super-Earths and Jovian planets, HATnet and SuperWASP produced more hot Jupiters, and interestingly, a couple sub-Earths may have been found around the nearby star Gliese 436. Spitzer provided us with the first detection of thermal radiation from a super-Earth (see here). A pair of M giants also became the first known to have planets, with planets reported around HD 208527 and HD 220074.

Circumbinary planets were announced around RR Cae, NSVS 14256825, Kepler-34 and Kepler-35 and Kepler-38, which is notable as the first Neptune-sized circumbinary planet.

Kepler results picked up en masse this year. At first it started out nice and slow, with small groups of planets being announced in batches (See here, here, here and here), followed by dozens and dozens of planets.

Interesting Kepler results included Kepler-64, the first quadruple-star system with a planet. The planet is a circumbinary planet, no less. But easily the most important circumbinary planet find was Kepler-47, the first transiting multi-planet circumbinary system. Multi-planet circumbinary systems have been found before but this is the first to have multiple planets transiting. This allows not only for their existence to be much more certain (non-transiting circumbinary planets still suffer from the mass-inclination degeneracy), but allows us to test for coplanarity. The Kepler-47 system demonstrates conclusively that short-period binary stars can host full systems of planets. Another pair of planets with very close orbits to each other, yet very dissimilar densities were reported at Kepler-36. The orbits of the planets in the Kepler-30 system were shown to be well-aligned with their host star’s equator, showing us that systems of planets are, like ours, often neatly arranged and not chaotically scattered.

Good news and bad news about the Kepler spacecraft. The good news is that the mission is extended for another three years. The bad news is that unfortunately, a reaction wheel on the Kepler spacecraft failed, and the mission’s continued usefulness now rests on all of the other reaction wheels remaining operational.

Kepler also unveiled a system of three sub-Earth planets huddled around a dim red dwarf, Kepler-42, which is very similar to Barnard’s Star, as well as a possible small terrestrial planet being evaporated away due to the heat from its star (see here). One of these three planets is Mars-sized(!).

We gained more evidence that the Galaxy is just drowning in planets both from continued Kepler results, HARPS results, and from gravitational microlensing data. Kepler showed us that hot Jupiter systems are frequently lacking in additional planets.

Last but not least, habitable planet candidates were reported around Gliese 163 and HD 40307, with unconfirmed habitable planet candidates reported at Tau Ceti and Gliese 667 C – with two more planets possibly occupying the star’s habitable zone. If GJ 667 Ce is confirmed, then it would be the most promising habitable zone candidate to date, based on its low mass.

At the end of 2011, I gave some wild guesses as to how the extrasolar planet landscape would look like at the end of 2012. Here we are and how have those predictions held up?

The Extrasolar Planets Encyclopaedia lists 854 planets as of the time of this writing, however it is missing quite a few. My own count has us at 899 planets.

  • The discovery of a ring system around a transiting planet

There are hints of ring systems (or perhaps rather circumplanetary disk systems) around Fomalhaut b, β Pictoris b, and 1SWASP J140747.93-394542.6 b (see here) but none of these are confirmed. So I’m calling it a missed prediction.

  • More low-mass planets in the habitable zone from both radial velocity and transit

Two new habitable planet candidates from radial velocity, none from transit.

  • Confirmation of obvious extrasolar planet atmospheric variability (cloud rotations, etc).

I was counting on continued monitoring of the HR 8799 planets to search for atmospheric variability, but it simply didn’t happen (or rather, if it did happen, the results are still pending). So I’m calling this a miss.

2013 could be a very interesting year, especially for Kepler. It seems we are on the verge of finding a true Earth analogue. The detection rate of candidate habitable planets is picking up and we’re really starting to get a list of targets to follow-up in the next decade. Here’s some more brave guesses for the end of 2013:

  • 1200 Confirmed planets and planet candidates
  • A satellite of an extrasolar planet (an “exomoon”)
  • A confirmed ring system around an extrasolar planet
  • Phase curve mapping of a sub-Jovian planet

2012 Planets